Rollup merge of rust-lang#50809 - kennytm:show-cargo-lock-diff, r=alexcrichton

GitHub: Stop treating Cargo.lock as a generated file.

We do want to inspect the changes to Cargo.lock, hiding the diff by default would make it easier to miss important details like rust-lang#50629 (comment) and rust-lang#50696 (review)

Author: kennytm

.gitattributes

@@ -7,4 +7,4 @@
 src/etc/installer/gfx/* binary
 *.woff binary
 src/vendor/** -text
-Cargo.lock -merge
+Cargo.lock -merge linguist-generated=false